1 To identify and characterize respiratory viruses of public health concern circulating in Bangladesh/ 1.1 To identify circulating influenza virus strains, clusters of severe respiratory disease and describe their etiologies. 1.2 To describe the genetic diversity of circulating RSV and rhinoviruses detected among hospitalized children with acute respiratory illness in Bangladesh 1.3 To assess the burden of respiratory virus infections in the first 2 years of life of children in Bangladesh and the impact on development of recurrent wheezing or asthma by 5 years of age 1.4 To describe the viral etiology of pneumonia and associated outcome in severely malnourished children in Bangladesh 1.5 To describe the seasonality and incidence of non-influenza respiratory viruses 2.1 To characterize the epidemiology and clinical presentation of seasonal influenza in Bangladesh, with particular emphasis on high risk groups 2.2 To identify modifiable risk factors for severe outcome (hospitalization and death) of acute respiratory illness (ARI) in adults and children (>5yo) 2.3 To characterize the complications due to influenza-associated acute respiratory illness among patients > 40 years of age 2.4 To characterize the causal association between influenza infection and symptomatic illness in hospitalized children <5yo and the association between micronutrient deficiency and respiratory illness in children <5yo 2.5 To assess the cost and impact of influenza illness during pregnancy on the health of mothers and their young infants (<6 mo age) in Bangladesh 2.6 To determine the incidence, clinical presentation and risk factors of secondary influenza infection in households. 3.1 To detect and respond to public health threats caused by avian influenza viruses 3.2 To characterize the incidence of laboratory confirmed avian influenza A virus infection among poultry workers and their protective humoral and cellular immune response as well as to characterize genetically the viruses causing the infections. 3.3 To describe the natural history of avian influenza virus infections in humans and to identify therisk factors for human disease caused by avian influenza infections (including H5N1) in Bangladesh 3.4 To design and pilot live bird processing workstations to improve hygiene practices in live bird markets